Tumor Treating Fields (TTFields) are low intensity alternating electric fields (e.g., 1-3 V/cm) in the intermediate frequency range (e.g., 125-250 kHz, or in some cases 100-500 kHz) that target solid tumors by disrupting mitosis. TTFields are typically delivered through two pairs of electrode arrays. The electrode arrays that make up each of these pairs are positioned on opposite sides of the body part that is being treated. FIGS. 1A and 1B depict the conventional positioning of electrode arrays on a subject's head and thorax, respectively. In each of these examples, a first pair of electrode arrays includes one electrode array at an anterior position 16/19 and a second electrode array at a posterior position (not shown, but located directly behind the corresponding anterior position). When an AC voltage is applied between the anterior electrode array and the posterior electrode array, the field lines of the resulting electric field will run generally between the front and the back of the subject.
Each of the FIGS. 1A and 1B examples also includes a second pair of electrode arrays including one electrode array at a right-side position 14/17 and a second electrode array at a left-side position 15/18. When an AC voltage is applied between the right-side array and the left-side array, the field lines of the resulting electric field will run generally between the left and right sides of the subject. AC voltages are applied in an alternating sequence between (i) the anterior/posterior (A/P) electrode arrays and (ii) the right/left (R/L) electrode arrays so that the direction of the field will switch repeatedly (e.g., every 1 sec.) between the two directions described above.
While the A/P and R/L electrode arrays are well suited for applying electric fields in two roughly perpendicular directions into many portions of a subject's body, a number of situations can be envisioned in which A/P and R/L electrodes may be difficult or impossible to use. Examples include situations in which a subject has a sore or ulcer at one of the commonly-used sites for positioning an electrode array, as well as treating tumors at locations where using both A/P and R/L electrodes would be uncomfortable and/or impractical (e.g., in a subject's neck, elbow, knee, etc.).